This invention relates to a low density microcellular foam, and more particularly, to a low density foam having a cell size of not greater than 2 .mu.m and to a method for making such small cell size, low density foam.
Conventionally known foams, such as polystyrene, polyurethane, polyethylene, etc., can be obtained in low densities between 0.01 and 0.1.times.10.sup.3 kg/m.sup.3. However, the cell size is generally too large, 200 .mu.m and above. Other foams produced by the same expansion techniques have similar cell sizes. To achieve small uniform cells, the number of nucleation sites must be increased so that more smaller cells develop. One foam of this type is Pneumacel, made by E. I. duPont de moures Co. which has a density of 0.02.times.10.sup.3 kg/m.sup.3 and cells that are about 25 .mu.m in diameter. Foams have been reported in the published literature that have cells a few micrometers in diameter, but have high densities. Various metods have been utilized to produce low density foam, as exemplified by U. S. Pat. No. 3,849,350 issued Nov. 19, 1974. However, a need exists in the art for a small cell size, low density foam and method of fabricating such.